OSI reference model was devised by ISO for effective
and smooth creation and functioning of any network.

This model has seven layers.

Physical layer: This layer
basically deals with physical, electrical and
mechanical specifications of a network model. It
accepts raw bit streams and passes it through
physical medium to the receiver.

Data link layer: This layer accepts
raw bit stream from physical layer and convert it
into meaningful information i.e. frames. This layer
deals with point to point connection. It also looks
after the error control and flow control of the
information.

Network layer:
This layer basically deals with routing of the
information (packets) received from transport layer
through either connection oriented virtual circuit
or connectionless Datagrams. It also takes care of
congestion control mechanism within the network.

Transport layer:
The functioning of transport layer is almost similar
to data link layer, where data link layer perform
point to point connection, transport layer deals
with end to end connectivity. It offers connection
oriented service to the upper layers.

Session layer:
This layer establishes session between sender and
receiver before the actual transmission. It makes
compatibility between two sources working at
different platforms.

Presentation layer:
This layer deals with syntax and semantics of the
information being transferred. It helps in
interoperability of different encoding methods. It
also deals with encryption and compression of data.

Application layer:
This layer enables the end user to access the
network. It provides user interface and support for
services such as e-mail, file transfer, remote log
in and shared database management etc. Famous
protocols used by this layer to offer these services
are SMTP, FTP, TELNET, DNS etc.